Measurements of heart chamber pressure, e.g., left atrial pressure (LAP), are useful for monitoring heart failure. If the LAP is abnormally high, a human patient will experience fatigue, shortness of breath, fluid build up in multiple areas of the body, and weight gain. Implantable pressure sensors (e.g., piezoelectric crystals and optical, capacitance, inductance, electrolytic, and/or resistive strain gauge manometers) are available to measure LAP so necessary medications can be taken to thus form a closed loop treatment system for managing heart failure. Due to tissue growth around the implanted sensor, electrical and mechanical shock, changes of ambient pressure, material creep, and aging of components, an implanted pressure sensor may drift and have an offset that may skew the pressure data measured by the implanted pressure sensor.
If the pressure reading is skewed, the patient may not get the proper treatment. As such, there is a need to ensure the pressure measured by the implanted sensor is the actual pressure within the heart. Thus, the implantable cardiac pressure sensor needs to be calibrated periodically after the implantation.
In one calibration method and apparatus, it is required that an implanted pressure sensor be exposed to atmospheric pressure in order to calibrate the sensor, thus requiring an invasive and/or uncomfortable procedure to access the sensor. As such, there is a need for a calibration method and apparatus of an implantable pressure sensor that minimizes patient discomfort, is not invasive, and/or does not require a percutaneous access to the sensor in order to calibrate it.
In one non-invasive calibration method and apparatus, a human patient is required to perform multiple Valsalva maneuvers for 8-10 seconds to complete the calibration of an implanted pressure sensor. However, in this method and apparatus, it is difficult (or impossible) for the patient with heart failure having an episode of congestive heart failure exacerbation with pulmonary edema to perform multiple Valsalva maneuvers due to symptoms of the disease. In addition, the patient may be subject to the risk of cross infection from the tubes and/or chambers utilized by the calibration apparatus if the apparatus is shared. On the other hand, if the patient applies too much pressure while doing the Valsalva maneuvers, the patient may feel dizzy or faint, get a hernia, damage alveolar sacs within the lungs, and/or get a punctured lung.
Accordingly, there is a need for an economical, repeatable, and non-invasive method and apparatus for the calibration of implanted pressure sensors that can minimize patient discomfort and the risk of infection.